The present invention relates to carburetors for two cycle engines, and more particularly to a carburetor and air-valve assembly and linkage.
Two-cycle engines are desirable for handheld tools where weight is critical because of their high power to weight ratio as compared to four-cycle engines. However, trapping efficiency of conventional two-cycle engines will not meet the low emissions requirements set forth by government regulations in the future because the fundamental design of the two-cycle engine results in too much unburned fuel being discharged into the atmosphere.
The discharge of raw, unburned fuel into the atmosphere is substantially caused by the exhaust and transfer ports being opened and closed by the piston, and for a small period both are open simultaneously during the piston travel. During that small duration of time, when both the intake and exhaust ports are open, the unburned fuel can exit the engine, which increases the measured emissions output of the engine while decreasing the engine""s efficiency.
The present invention provides a carburetor and air valve assembly for a two-cycle internal combustion engine with stratified air scavenging, the assembly comprising: a housing assembly; an intake channel in the housing assembly for delivering fuel and air mixture to an intake port of the engine; a throttle valve disposed within the intake channel and fixed to a pivotable throttle valve shaft; a throttle lever fixed to the throttle valve shaft; an air channel in the housing assembly for delivering fuel-free air to an airport of the engine; an air valve disposed within the air channel and fixed to a pivotable air valve shaft; an air valve lever fixed to the air valve shaft, and an activating lever moveably mounted to the housing assembly and adapted to transmit movement of the throttle lever to the air valve lever.
According to another aspect, the present invention provides a two-cycle internal combustion engine system comprising: a carburetor comprising an intake channel, a choke valve in the intake channel fixed to a pivotable choke valve shaft and a throttle valve in the intake channel fixed to a pivotable throttle valve shaft; an air channel in communication with fresh air and comprising an air valve fixed to a pivotable air valve shaft; a cylinder; a combustion chamber within the cylinder; a fuel port communicating the intake channel with the cylinder; an air port communicating the air channel with the cylinder; a piston arranged for reciprocating movement within the cylinder and comprising a transfer port for intermittently connecting the fuel port and air port with the combustion chamber; a throttle lever fixed to the throttle valve shaft; an air valve lever fixed to the air valve shaft; an activating lever pivotably mounted to the air valve shaft and adapted to transmit movement of the throttle lever to the air valve lever after a predetermined angle of rotation of the throttle lever; a choke valve lever fixed to the choke valve shaft; and a fast idle latch engagable by the choke valve lever to hold the throttle lever in a fast idle position until the throttle lever is separately moved.